Increasingly, microbeams and microcrystals are being used for macromolecular crystallography (MX) experiments at synchrotrons. However, radiation damage remains a major concern since it is a fundamental limiting factor affecting the success of macromolecular structure determination. The rate of radiation damage at cryotemperatures is known to be proportional to the absorbed dose, so to optimize experimental outcomes, accurate dose calculations are required which take into account the physics of the interactions of the crystal constituents. The program RADDOSE‐3D estimates the dose absorbed by samples during MX data collection at synchrotron sources, allowing direct comparison of radiation damage between experiments carried out with different samples and beam parameters. This has aided the study of MX radiation damage and enabled prediction of approximately when it will manifest in diffraction patterns so it can potentially be avoided. However, the probability of photoelectron escape from the sample and entry from the surrounding material has not previously been included in RADDOSE‐3D, leading to potentially inaccurate does estimates for experiments using microbeams or microcrystals. We present an extension to RADDOSE‐3D which performs Monte Carlo simulations of a rotating crystal during MX data collection, taking into account the redistribution of photoelectrons produced both in the sample and the material surrounding the crystal. As well as providing more accurate dose estimates, the Monte Carlo simulations highlight the importance of the size and composition of the surrounding material on the dose and thus the rate of radiation damage to the sample. Minimizing irradiation of the surrounding material or removing it almost completely will be key to extending the lifetime of microcrystals and enhancing the potential benefits of using higher incident X‐ray energies.

中文翻译：

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用于微束和微晶的实验剂量：RADDOSE-3D中的蒙特卡洛模拟。

微束和微晶越来越多地用于同步加速器的大分子晶体学（MX）实验。但是，辐射损伤仍然是主要问题，因为它是影响大分子结构测定成功的基本限制因素。众所周知，低温下的辐射损伤率与吸收剂量成正比，因此，为了优化实验结果，需要进行精确的剂量计算，其中要考虑到晶体成分相互作用的物理性质。RADDOSE-3D程序可估算在同步加速器源处MX数据收集期间样品吸收的剂量，从而可以直接比较使用不同样品和光束参数进行的实验之间的辐射损伤。这有助于研究MX辐射损伤，并能够预测其何时会以衍射图样出现，从而有可能避免。但是，RADDOSE-3D以前并未包括光电子从样品中逸出和从周围材料进入的可能性，从而导致使用微束或微晶进行实验的估计可能不准确。考虑到样品和晶体周围材料中产生的光电子的重新分布，我们提出了RADDOSE-3D的扩展，该扩展在MX数据收集期间执行旋转晶体的蒙特卡洛模拟。除了提供更准确的剂量估算值外，蒙特卡洛模拟强调了周围材料的尺寸和成分对剂量的重要性，因此也说明了辐射对样品的破坏率。最大限度地减少对周围物质的辐射或将其几乎完全去除，对于延长微晶的寿命和增强使用更高入射X射线能量的潜在益处至关重要。